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Digital Pressure and Temperature Sensor

 

 

 

 

Introduction 

Stevens Smart PT is an advanced digital pressure and temperature sensor ideal for water 

level measurements as well as many other types of pressure and fluid level monitoring 

applications. The SDI-12 communications interface provides universal compatibility with 

industry standard data loggers. 

In addition to simple instantaneous pressure, level, and temperature measurements, Smart 

PT includes the ability to automatically record peak crest levels, calculate average level as 

well as standard deviation all without complex datalogger configurations. Other advanced 

features include adjustable fluid density, automatic water temperature density 

compensation, and adjustable local gravity compensation. 

An M14-1 threaded sensor head allows for easy mounting to pipes. An included threaded 

cap offers a loop hole which can be used to mount weights or pull the sensor through pipes 

or other small areas. The Smart PT is built to last for years in the field with fully sealed and 

potted components, a robust ceramic membrane, stainless-steel housing, and an industrial-

quality cable. 

 

 

 

 

Summary of Contents for Smart PT

Page 1: ...o automatically record peak crest levels calculate average level as well as standard deviation all without complex datalogger configurations Other advanced features include adjustable fluid density automatic water temperature density compensation and adjustable local gravity compensation An M14 1 threaded sensor head allows for easy mounting to pipes An included threaded cap offers a loop hole whi...

Page 2: ...ced SDI 12 Commands 9 Configuring pressure depth and temperature units 9 Configuring gravity compensation 10 Configuring density compensation 11 Configuring the Smart PT for top of casing or reference relative measurements 11 Restoring the Smart PT to the default configuration 13 Using the Smart Sampling features and digital crest gage mode 14 Example configurations for average and daily maximum 1...

Page 3: ... depends on elevation and atmospheric pressure 51168 303 1 4 4 13 90 51168 304 2 10 33 140 51168 305 4 30 100 240 51168 306 10 90 300 390 51168 307 20 190 630 390 32142 Recommended Yearly Calibration Performance Characteristics Parameter Unit Pressure accuracy 0 1 Full scale Long term stability max 0 15 per year Full scale Temperature accuracy 0 25 C Average current consumption SDI 12 0 9 mA Avera...

Page 4: ...ube The vented version of the Smart PT has a tube running the length of the cable This allows the water pressure on the front of the transducer to reference against barometric pressure The Smart PT ships with a black cap over end of the vent tube to prevent moisture ingress and with a separate desiccant capsule Before installation the dessicant capsule needs to be connected and the yellow cap remo...

Page 5: ...alibrated every year Before returning the sensor for calibration or repair navigate to the Support page at http www stevenswater com and fill out the RMA form If the sensor was used in contaminated water the sensor must be cleaned before shipping Coil and zip tie the sensor cable before shipping ...

Page 6: ...ast few digits of the pressure reading Basic SDI 12 Commands Command Response Description a a CR LF Acknowledge active a sensor address aI a14ccccccccmmmmmmvvvxxx xx CR LF Example Vented 014STEVENSW_SVP01_VT_1234567890 Non vented 014STEVENSW_SVP01_NV_1234567890 Send identification a sensor address 14 SDI 12 protocol version ccc manufacturer identification mmm sensor identification vvv sensor versi...

Page 7: ... min and max since the last M1 command a sensor address min lowest pressure encountered since last M1 reading max highest pressure encountered since last M1 reading tmin seconds elapsed since the minimum reported in min tmax seconds elapsed since the maximum reported in max See the section Using Excel to extract timestamped crest values from a data set for more information on using tmin and tmax a...

Page 8: ...Send average and standard deviation since the last M2 command a sensor address avg average of all pressure samples taken since the last M2 reading stddev standard deviation of all pressure samples taken since the last M2 reading nsamples number of samples taken since the last M2 reading ...

Page 9: ...d Smart PT only reports in units of pressure Because it measures the weight of the water column plus the atmosphere it wouldn t be useful to report units of depth Command Response Description aXR_PUNITS aPUNITS UUU CR LF Example aXR_PUNITS aPUNITS M Query pressure units UUU pressure units aXW_PUNITS_UUU aPUNITS UUU CR LF Example aXW_PUNITS_M aPUNITS M Configure pressure units uuu pressure units me...

Page 10: ...l gravitational acceleration https www wolframalpha com input i gravity portland oregon When the Smart PT is configured to report in units of pressure rather than depth no gravity compensation will be applied Command Response Description aXR_GRAVITY aGRAVITY vvv CR LF Example aXR_GRAVITY aGRAVITY 9 80665 Query gravity a sensor address vvv gravitational acceleration aXW_GRAVITY_vvv aGRAVITY vvv Exa...

Page 11: ...sity a sensor address vvv density Default 1 g mL Configuring the Smart PT for top of casing or reference relative measurements The Smart PT can be configured to report depth measurements from actual or surveyed top of casing Following this command table is an example Command Response Description aXR_TOC_vvv aTOC vvv CR LF Query top of casing aXW_TOC_vvv aTOC vvv Example aXW_TOC_1 aTOC 1 If non zer...

Page 12: ... set the offset parameter to 15 The Smart PT will report the sensed depth plus the offset for a reported value of 70 aXW_OFFSET_15 To report distance from water to top of casing set toc to 75 The Smart PT will return the TOC value minus sensed depth for a reported value of 20 aXW_TOC_75 To report distance from the water surface to bottom of well set offset to 25 The Smart PT will return the sensed...

Page 13: ...ion It may be useful to restore the Smart PT to the factory default configuration Command Response Description aXD_ arestore factory configuration Restore the sensor to a factory default state Stored data will be lost Sensor retains factory calibration ...

Page 14: ...s also able to report average and standard deviation over the logging interval This may be useful for integrating data from rough water and quantifying surface roughness Instead of a sliding window the Smart PT uses a numerically stable online variance algorithm Welford 1962 to maintain the mean and standard deviation since the last time those values were queried Example configurations for average...

Page 15: ...he event occurred In the example below a crest event occurred at 8 24 20 AM The sensor was polled by a datalogger at 8 30 00 AM at which time the sensor reported the crest event as happening 340 seconds in the past Logger timestamp Min Max tMin tMax Time of crest A3 TIME 0 0 E3 8 30 00 AM 1004 4996 33 340 8 24 20 AM 8 40 00 AM 1004 4995 23 324 8 34 36 AM 8 50 00 AM 1003 4999 47 310 8 44 50 AM 9 00...

Page 16: ...B Calculation of depth Depth is computed as follows depth depth 9 80665 gravity 1000 density If density is set to 1 the Smart PT will apply a temperature correction density 999 83952 16 945176 t 0079870401 t t 0 000046170461 t t t 0 00000010556302 t t t t 0 00000000008054253 t t t t t 1 016897850 t If density is set to a value other than 1 that value will override the temperature correction If top...

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